IBU refer to the North American (ASBC) way of specifying bitterness. While they are intended to convey perceived bitterness they are roughly equivalent to mg/L isomerized bittering principal per Liter of beer. To measure them one puts 10 ml of beer into a centrifuge tube transferring it in a pipet that has been dipped in octanol (to flatten any foam), adds 1 mL 3N HCl and 20 mL spectrophotometric grade iso-octane and shakes vigorously for 15 minutes. The bittering materials will be extracted into the gasoline (iso octane). Sometimes a sludge forms and centrifugation for the minimum time required to separate the gasoline phase is employed. A sample of the gasoline phase is put in a 1 cm cuvette and its absortion measured at 430 nm against iso-octane with a minute amount of octanol. The absorption multiplied by 50 is the IBU value.

In Europe the EBC procedure is almost identical except that no octanol is involved, 0.5 mL of 6N hydrocloric acid is used, the shaking is done with 3 small glass balls added and the sample is always centrifuged for 3 minutes before the reading is taken. Measurement is in 1 cm at the same wavelength and, again, the absorption is multiplied by 50 to give the BE (Bittereinheiten) - at least that's what it's called in German but Analytica EBC is also in English (where it probably called EBUs) .

Because the absorption decreases pretty quicly with time at the completion of extraction the EBC reported value will, in general, be a litttle smaller than ASBC reported value unless the beer requires centrifugation. For all practical considerations the two systems should give the same results.